Air-conditioning systems are commonly provided to provide heating and cooling to a space. A compressor unit is provided to compress and thereby heat refrigerant which is provided thereto in a gaseous state. The compressed a heated refrigerant is passed through condenser coils, where air is forced over them to release heat into the atmosphere, thereby condensing the refrigerant to liquid form. The liquid refrigerant may pass through a metering device, which regulates the flow of refrigerant while lowering its pressure, then entering an evaporator, which is located in or near a space to be cooled. Air from the space is forced over evaporator coils, which causes heat from the space to be absorbed by the refrigerant, which becomes a gas. The gaseous refrigerant is then carried to the compressor unit, where the cycle starts again.
To provide heating, the direction of flow is reversed. A reversing valve is provided in order to ensure that the direction of flow through the compressor unit remains the same as when cooling.